The Internet of things (IoT) is the inter-networking of physical devices, vehicles, buildings, and other items embedded with electronics, software, sensors, actuators, and network connectivity that enable these objects to collect and exchange data. IoT is expected to offer advanced connectivity of devices, systems, and services that goes beyond machine-to-machine (M2M) communications and covers a variety of protocols, domains, and applications.
IoT can be encapsulated in a wide variety of devices, such as heart monitoring implants, biochip transponders on farm animals, automobiles with built-in sensors, automation of lighting, heating, ventilation, air conditioning (HVAC) systems, and appliances such as washer/dryers, robotic vacuums, air purifiers, ovens or refrigerators/freezers that use Wi-Fi for remote monitoring. Typically, IoT devices encapsulate wireless sensors or a network of such sensors.
Most IoT devices are wireless devices that collect data and transmit such data to a central controller. There are a few requirements to be met to allow widespread deployment of IoT devices. Such requirements include reliable communication links, low energy consumption, and low maintenance costs.
To this aim, an IoT device and wireless sensors are designed to support low power communication protocols, such as Bluetooth Low Energy (BLE), LoRa, and the like. To achieve low power consumption, at the physical layer, a wireless BLE-compliant device can be configured as a transmitter or a receiver. That is, a device can be implemented only a transmitter or a receiver. At the Link Layer, devices are divided into advertisers, scanners, slaves, and masters. An advertiser is a device that transmits packets; a scanner is a device that receives the advertiser's packets. A slave is connected to a master. Typically, advertisers and slaves have the lowest possible memory and processing burden, thus demonstrating low power (energy) consumption.
On the other hand, the scanners and masters perform most of the processing and, thus, are equipped with batteries, user interfaces, and possibly even an electricity supply. In an IoT network (i.e., a network of IoT devices), a typical design would be to shift most processing tasks from slaves to masters and from advertisers to scanners. Such a design would reduce the power consumption of the most resource-constrained devices and shift the burden to the most resource-intensive devices.
Modulated backscattering is a transmission technique utilized to reduce communication power consumption at the sensor node when compared to a conventional RF transmitter. Backscatter modulation allows a remote device to wirelessly telemeter information without operating a traditional transceiver. In conventional solutions, a backscatter device leverages a carrier transmitted by an external source (i.e., external to the backscatter modulator and the receiver). For example, an access point, a base station, or a dedicated transmitter can be used to transmit the carrier.
Conventional solutions for backscattering BLE packets operate based on the premise that the data can be transferred in broadcast “advertising packets” without requiring acknowledgements. Further, the three advertising channels defined in the BLE standard use a fixed modulation scheme in three fixed frequency channels centered on 2402 MHz, 2426 MHz, and 2480 MHz. Furthermore, every BLE receiver listens for incoming advertising packets across all three advertising channels and, thus, reception of advertising packets on any one channel is sufficient for the message to be received.
As illustrated in FIG. 1, existing solutions for backscattering BLE packets require a continuous wave (CW) radio frequency (RF) source 110 to be present in the environment at a specially chosen frequency. A modulated backscattered (MBS) transponder 120 receives the CW signals and generates a backscattered spectrum including a band-pass signal in each of the BLE advertising channels in sequence. The band-pass signal is modulated using a binary frequency-shift keying (FSK) scheme at a predefined rate and formatted as BLE advertising packets. The BLE advertising packets are transmitted by the backscattered transponder 120 and received at a BLE receiver 130 (e.g., a smartphone). Typically, the backscattered transponder 120 includes a single field-effect transistor (FET, not shown) driven by a baseband source signal.
The disadvantage of the solution demonstrated above is that CW signals are generated by an additional external transmitter (an external source). Further, the modulation of the backscattered signals is performed using a CW signal having a frequency of 2.4 GHz, which is a congested frequency band due to, e.g., Wi-Fi signals.
Another backscatter technique utilized in Wi-Fi networks is based on piggybacking the backscattered signals on existing Wi-Fi transmissions using a non-standard protocol stack. Such a technique is very complicated to implement and requires hardware and software modifications to devices that receive and transmit backscatter signals.
It would therefore be advantageous to provide a solution for backscattering packets transmitted over wireless medium that would overcome the deficiencies noted above.